Refuse converting method and apparatus utilizing long arc column forming plasma torches

ABSTRACT

A method and apparatus are disclosed which are based on utilizing a plural number of long arc column forming plasma torches in combination with a refractory lined furnace chamber to continuously pyrolyze household and industrial refuse material fed into the chamber and convert the same to usable materials and useful forms of energy.

O Umted States Patent [1 1 [111 3,779,182

Camacho 1 Dec. 18, 1973 REFUSE CONVERTING METHOD AND 3,173,388 3/1965Menrath et a1 110/8 E APPARATUS UTILIZING LONG ARC 3,503,347 3/1970Marr, Jr et al..... 110/8 R 3,404,078 10/1968 Goldberger 219/121 PCOLUMN FORMING PLASMA TORCHES 3.290.552 12/1966 Van Ornum 219/75Salvador L. Camacho, ONeal Rd, Raleigh, NC. 27602 Filed: Aug. 24, 1972Appl. No; 283,516

lnventor:

US. Cl 110/8 R, llO/l8 E, 110/8 E, 219/121, 219/75 Int. Cl. F23g 5/12Field of Search 110/8 R, 8 E, 18 C, 1 10/8 C, 18 E; 219/12], 72-75, 383

References Cited UNITED STATES PATENTS 11/1970 Zanft 110/8 R PrimaryExaminerl(enneth W. Sprague Assistant Examiner-Henry C. Yuen Ar!0rne vB.B. Olive [57] ABSTRACT A method and apparatus are disclosed which arebased on utilizing a plural number of long are column forming plasmatorches in combination with a refractory lined furnace chamber tocontinuously pyrolyze household and industrial refuse material fed intothe chamber and convert the same to usable materials and useful forms ofenergy.

10 Claims, 4 Drawing Figures REFUSE CONVERTING METHOD AND APPARATUSUTILIZING LONG ARC COLUMN FORMING PLASMA TORCI-IES CROSS-REFERENCE TORELATED APPLICATIONS This invention is related to copending application,Serial No. 283,552, entilted Trough Hearth Construction And Method ForPlasma Arc Furnace, which discloses an electric circuit for initiatingand sustaining long arc plasma columns utilizing long are column formingplasma generators or torches of the type previously taught in U.S. Pat.No. 3,673,375, entitled Long Arc Column Plasma Generator and Method,"issued to the same inventor.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to methods and apparatus for. reducing the physicalweight and volume of refuse by'subjecting it to direct radiated. andconvected heat from a long plasma arc column.

2. Description of the Prior Art 7 Pyrolysis (or destructivedistillation) techniques were until very recently unrecognized 'as ameans for. converting'municipal and industrial refuse into useful solid,liquid and gaseous products. In the past, conventional incinerators havebeen widely used to reduce refuse to ash through combustion. Thisprocess necessarily introduced fly. ash and many other types of airbornepollutants into the' atmosphere, due to the tremendous amounts of airutilized to effect combustion. vAs an alternate measure, sanitarylandfills were developed to prevent air pollution. It is now recognized,however, that water leaching through such landfills may constitute apollutant to ground water. It is a well-known and documented fact thatrefuse contains both combustible and non-combustible materials. TheUniversity of California, as a result of a study analyzing municipalrefuse, has stated that the composition of municipal mixed"(unsegregated) refuse by weight is: cans, 9.8 percent, bottles andglass, 1 1.7 percent; metals (other than cans) 0.9 percent; other 77.6percent. (See University of California Technical Bulletin No. 9,Sanitary Engineering Laboratory 1973 American Public Works Association,."Municipal Refuse Disposal). It is also a well-known fact that thenon-combustible portion which approximates 25 percentof the total weightof refuse is never appreciably reduced by either conventionalincineration or landfill practices. Typically, these items are eithershredded and buried at the landfill or are simply heaped near theincinerator.

In its I970 study entitled Conversion of Municipal and Industrial Refuseinto Useful Materials by Pyrolysis, the United States Department of theInterior, Bureau of Mines, revealed the usefulness of pyrolyzing refuseand obtaining usable solid, liquid, and gaseous products. In this study,various samples of shredded municipal and industrial refuse with themetallic component largely removed were placed in a sealed retort andsubjected to various levels of conducted heat to as much as 900centigrade. Among the resulting products were solid residue (a source ofcharcoal briquettes and filter medium), propane, ethylene and methanegas, solid ammonium sulphate, tar, light oil (a soure of benzene andtoluene) and liquor 95 percent water and the remainder formed of acids,ketones and aldehydes). In

terms of recoverable heat energy, the products of pyrolysis of refuseproduced more than a sufficient Btu content to provide the heat forpyrolysis. (See W. S. Sanner et al.: Conversion of Municipal andIndustrial Refuse into Useful Materials by Pyrolysis," Report ofInvestigations No. 7428, U.S. Department of the Interior, Bureau ofMines, August, 1970.)

Although the study conducted by the Bureau of Mines was instrumental indetermining the potential value of converting refuse into usableproducts by pyrolysis, it did not suggest an efficient method andapparatus to do so. The system used was based upon a batch method ofcharging the retort and did not suggest a method and apparatus for moreefficient continuousoperation. Furthermore, the solid residue containedbottle caps and bits of metal which required further separation beforethe solid residue could be utilized. In addition, the bulk of themetallic refuse component was required tobe segregated from thecombustible or carbonaceous component prior to pyrolysis, and thecombustible component required drying and shredding. for maximumefficiency of the process.

Additional prior art has suggested the use of conventional arc-formingelectrodes. in an incinerator in U.S. Pat. No. 3,503,347 tointermittantly generate heat and thereby reduce the volume and weight ofwaste confined inside the incinerator. The above patent does not,however, teach the continuous operation of such an incinerator and doesnot teach a practical application of the evolved noxious gases. Ingeneral, the prior art has not suggested an efficient method andapparatus utilizing long arc column plasma torches for reducingsubstantially large amounts of unsegregated refuse to usable andvaluable products from which energy may be readily obtained, while atthe same time not polluting the environment. Furthermore, the prior arthas not suggested such a method and apparatus which would be adapted forcontinuous rather than batch operation and capable of reducing thephysical weight and volume of substantially large amounts of refusewhile generating more energy than being consumed.

SUMMARY OF THE INVENTION This invention utilizes a plurality of long arecolumn forming plasma torches in combination with a furnace chamber tothermally decompose unsegregated refuse into a gaseous and molten fluidstate. Conveyor means are adapted to continuously supply refuse to thefurnace chamber while smoke recycling means are adapted to prevent thegases being produced within the chamber from escaping. The furnacechamber is formed so as to have a somewhat bowl-shaped refractor linedinterior hearth portion into which the long are forming plasma torchesare directed. The hearth portion further includes a normallyelectrically disconnected graphite electrode but which may beappropriately connected into the electrical circuit when needed as anelectrode. A lip formed along one edge of the refractory materialprovides a fluid outlet for the molten refuse. Pyrolysis of the refuseproceeds as long are plasmas are generated between the various torchesresiding in vertical wall portions of the furnace chamber, and moltenmetallic portions of the refuse collects in the hearth. The heatradiated and convected from the generated long are plasma columns issufficient to reduce the remaining organic and non-combustible portionof the refuse to either a molten or gaseous state. Some of the evolvedgases rise, preheat the refuse and are then reintroduced into thereduction process. In a preferred embodiment as the molten refusereaches the level of the outlet lip it is oxidized by an incoming streamof gas, e.g., air. The oxidized molten refuse then enters a water bathwhich effectively provides a water seal and forms into a solid slag forlater recovery by appropriate handling means. In some instances the slagmay be maintained heated for purposes of molding the same. The gaseousproducts of the pyrolyzed refuse are simultaneously converted intosaturated steam and other gases which may beneutralized or combusted byintroduction of gases other than thementioned air. The hot gases maythen drive appropriate energy conversion means such as a turbinegenerator and may be scrubbed or otherwise purified before beingreleased to the atomosphere.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional side view ofatypical refuse converting apparatus according to the invention.

FIG. 2 is a cutaway side view of a long arc column forming plasma torchemployed in the instant invention generally shown in operating positioninside a furnace chamber.

FIG. 3 is a top plan view of a refuse converting apparatus according tothe invention.

FIG. 4 is a somewhat schematic diagram of an electrical circuit employedin the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, aspreviously mentioned, the present invention is directed to an apparatusand method for continuously reducing by pyrolysis the physical weightand volume of municipal and industrial refuse material and converting itinto energy, recoverable and useful products, utilizing long are columnplasma generators, also known in the art as plasma torches. In apreferred embodiment, a complete refuse converting apparatus includes afurnace chamber a plurality of directionally stable long arc columnforming plasma torches, generally designated 12, of the type disclosedin previously referred to US. Pat. No. 3,673,375, projecting throughselected apertures 11 in vertical walls 14 of said furnace chamber 15.Also included is a somewhat concave refractory lined furnace hearth 17having an integrally formed graphite electrode 18. Said refuseconverting apparatus is also provided with a refuse hopper 20 includingsealed refuse conveying means 21 and smoke recovery means 23, togetherbeing adapted to continuously feed refuse materials into said furnacechamber 15, while maintaining smoke and noxious gases within thechamber. The term refuse as used in this disclosure includes rawunsegregated refuse of a municipal or industrial nature or any mixtureof both. By unsegregated" what is meant is that organic wastes are mixedwith tin cans, bottles, paper, etc.

In accordance with the instant invention during operation, laterdescribed in greater detail, each plasma torch 12 is adapted to form atransferred long arc column of from 10 to inches with molten refusematerial 19 a portion of which is metallic. Due to the intense heatbeing generated (1,000 to 2,000K), the nonmolten refuse (represented bydashed lines 22) is rapidly pyrolyzed into gaseous and molten fluidcomponents in the absence, at this point, of appreciable combustion.

Hot gases and molten refuse evolved from the heat of the arc columnsflow past a lip 16 formed in the concave refractory lined hearth 17 andinto an oxidation chamber 30 which includes a gas inlet manifold 31 foroxygen or air which enables the evolved gases to be combusted into anoxidation dioxide and steam vapor. Depending on the nature of the refusegases produced, gases other than air or oxygen may be introduced tocombust or neutralize such refuse gases. Gas vent 32 receives the hotcombusted vapor while a water bath 33 receives the molten residue andreduces it into a solidified slag material 38. The solidified slagaggregate is a highly salable item due to its silica and metalliccontent. A ridge of molded refractory material 34 adjacent lip 16further enhances combustion and further degradation of the molten refuseby increasing the surface area over which the refuse is exposed tooxidation. The action of the water seal with the molten refuse serves togenerate additional steam. A turbine generator 35, for example, mayreceive the hot gases entering gas vent 32 and be used to generate moreelectrical power than is consumed by the torches. Appropriate gastreatment means (not shown) receive and scrub the combusted gases untilsafe for release to atmosphere. Alternately, selected valuable gases,e.g., methane, may be separated by well-known means before beingcombusted by withdrawing a portion of the gas by appropriate means (notshown). The now solidified slag 38 may be handled by appropriate bladeor other suitable conveyor means 60 and finally withdrawn from the waterbath by additional handling apparatus 61 for later use.

Referring to FIG. 2, a long arc column plasma torch, according to theinvention and as previously taught in US. Pat. No. 3,673,375, is definedas being an apparatus and an electrical conductor in the arc circuit andincludes a cylindrical shaped electrode 36, a gas directing nozzle 37axially aligned with, forwardly spaced and insulated from electrode 36,and appropriate gas and electrical supply means (not shown). Aspreviously disclosed in copending application, Ser. No. 283,552 a pilotare indicated by dashed lines 45, may be struck between electrode 36 andnozzle 37 by introducing a current potential therebetween whilesimultaneously applying a vortical flow of gas directed outward throughsaid nozzle 37. Such a pilot arc is readily trans ferred to a metallicmaterial 46 also in the electrical circuit when such pilot are 45becomes proximate said metallic matter (i.e., 4-7 inches) byappropriately advancing said torch 12 into a position proximate saidmetallic refuse 46. In the instant invention, it has been recognizedthat such a long are column plasma torch has particular effectiveness ina refuse converting apparatus since one component (typically 25 percent)of refuse is metal.

Referring now to FIG. 3, a first long arc column plasma torch 40, inpreferred form, is adapted to extend through an aperture 47 in a portionof a rear wall 51 of said furnace chamber 15 while second 41 and third42 long are column plasma torches are adapted to extend throughapertures 48, 49 in adjacent corner wall portions 52 of said furnancechamber. As is perhaps apparent, many other torch mountingconfigurations will appear to those skilled in the art, and theparticular mounting details described herein are for purposes of exampleonly. A sleeve or collar 53 (FIG. 2) which may be stainless steel, forexample, lining each respective aperture 47, 48, 49 is adapted to enablehorizontal and vertical angular, as well as axial, movement of eachplasma torch within its respective mounting position while preventingheat and noxious gases from escaping through apertures 47, 48, 49.Remotely controllable torch positioning means 24 (FIG. 1) are providedto enable accurate positioning of the plasma torches.

Referring now to FIG. 4, 'as previously mentioned, each long arccolumnforming plasma torch utilized in the present invention (shown in crosssection) includes a cylindrical shaped internal electrode 36 and a gasdirecting nozzle 37 axially aligned with, forwardly spaced and insulatedfrom electrode and appropriate gas, water and electrical supply means(not shown). while the last mentioned gas and water supply meansareconsidered well-establishedin the art requiring no furtherelaboration herein, a better understanding may be gained of theinvention by a discussion'of its advantageous use of power in startingand maintaining the various long arc plasma columns. Utilizing a threephase A. C. wye 55 having a floating neutral 56 to conveniently supplypower to three long arc column forming plasma torches 12, a given torchinternal electrode 36 is connected to an individual current phase. It isapparent that if more than three torches are employed, a greater numberof phases may be utilized. Each torch nozzle 37 is connected to anadjacent phase 58 via an appropriate .choke 59. In this manner, apilotarc 45 may be struck between the nozzle 37 and internal electrode 36 ofeach torch without introducing a consumable electrical conductor byapplying the phase to adjacent phase voltage differential, causedbyvchoke 59, across internal electrode 36 and nozzle 37 and bysimultaneously introducing a gas vortical flow through nozzle 37. Thecurrent passing through the pilot arc 45- is substantially smaller thanthat of the main arc 13 (see FIGS. 1 and 2) which is subsequentlyadapted to be transferred to the metal scrap to be melted. Simultaneoustransferral of at least two pilot arcs 45 to the metallic refusecomponent establishes at least two main transferred arcs (not shown) andcompletes a phase 57 to adjacent phase 58 loop whereby the fullavailable current is now utilized.

Since the nature and physical arrangement of the refuse with respect tothe torches willvary widely during operation it is contemplated that oneor more torches may become inoperable. For example, a falling porcelaincoated refrigerator or a sudden deluge of rotten vegetables may stiflean are. In this event, any single torch may be operated phase to neutraland a new plasma column path may be established by restarting with apilot arc. Thus, when contact with an electrically conductive melt or anelectrically conductive unmelted refuse is lost to a particular plasmacolumn connection may be made to graphite electrode 18 to a ground orneutral 79 (FIG. 1) by a suitable manual or remotely operated contactor78. Once a molten metallic pool is reestablished the other torches maybe again utilized.

Once a molten pool 19 of metallic refuse has been formed and preferablyall long arc plasma columns 13 have made electrical contact with saidmolten pool, it is possible to then continuously dump unsegregatedrefuse 25 into the furnace chamber 15. The small molten metalliccomponent of the unsegregated refuse will then be sufficient to sustainelectrical connection between the three plasma arcs. Furthermore, theabove described method of operating long are column plasma torches inelectrical connection with a molten pool of metallic refuse 19 assurescontinuous operation of the furnace since the metal having a higherspecific gravity than the bulk of other refuse will tend to remain. inthe concave refractory lined hearth 17 while the continuously meltingmixed metallic-non-metallic refuse will tend to flow out of the concavefurnace hearth. 17, pass the outlet lip 16 through oxidation chamber30and into water bath 33. It is also a recognized. advantage of theparticular embodiment shown to utilize the hot gases being evolved inthe furnace chamber to pre-heat refuse materials 25 entering the furnacethereby promoting even greater efficiences. Based on the foregoinginvention operation parameters, the specific furnace design andconstruction is deemed well within the established electric arc furnaceart and therefore requires no further elaboration here. While specificrefuse conveying means, material handling and energy recovery means havebeen suggested, these aspects of the instant invention are alsowell-known in the established art. A- complete but not definitive methodof converting refuse into usable energy recoverable products based onthe described invention may include:

a. initially charging a furnace built in accordance with the inventionwith refuse having a high metallic content;

b. initiating and sustaining a plurality of long are plasma columns andreducing the largely metallic refuse to a molten pool;

c. conveying refuse of any class or mixture into the furnace;

d. reducing by heat pyrolysis the physical weight and volume of saidconveyed refuse into molten fluid and gaseous products;

e. converting the evolved molten fluid and gaseous products to usableenergy;

f. treating and purifying the final products before returning them tothe atmosphere.

On the basis of the foregoing description, it is apparent that theinstant invention provides an efficient and environmentally safealternative to landfill, and combustive incineration practices of refusedisposal while at the same time providing a source for energy throughthe use of long are column forming plasma torches. According to theinvention, it is now possible to continuously decrease the physicalweight and volume of raw unsegregated refuse while converting theevolved products to useful materials and useful energy.

What is claimed is:

1. An apparatus for reducing by pyrolysis raw unsegregated refusecomprising:

a. a furnace chamber;

b. a refractory lined hearth in said furnace chamber;

c. conveyor means adapted to introduce raw unsegregated refuse, at leasta portion of which is metallic, into said furnace chamber; and

d. long arc column forming plasma generator means mounted in saidchamber and adapted to initiate and sustain at least one long arc columnplasma having a portion thereof in electrical contact with said refuseand being adapted to reduce said refuse to gaseous and molten fluidproducts by utilization of the column heat.

2. The apparatus of claim 1 including gas supply means adapted tocontact and chemically react with said gaseous and molten fluidproducts.

3. The apparatus of claim 2 including energy conversion means adapted torecover energy from said products.

4. The apparatus of claim 2 wherein said gas supply means comprises anoxidizing supply.

5. The apparatus of claim 1 wherein said generator means comprises aplurality of peripherally spacedgenerators and including electricalcircuit means adapted to initiate a pilot arc in each said generator andenabling a main long are column to be transferred between at least twosaid generators and said refuse.

6. The apparatus of claim 1 including groundable electrode meansincluded in said hearth and being adapted to enable a long are plasmacolumn to be generated between at least one said generator and saidgrounded electrode.

7. A method for reducing by pyrolysis a volume of raw unsegregatedrefuse comprising:

a. initially charging a furnace chamber with refuse materials of which asubstantial portion is metallic;

b. providing long plasma arc column generation means extending throughat least one wall portionof said furnace chamber;

c. establishing and maintaining at least one long plasma arc columnbetween said generation means and said refuse thereby reducing by heatat least said metallic refuse portion to amolten state;

d. conveying additional raw unsegregated refuse into said furnacechamber; and

e. pyrolyzing all of said raw unsegregated refuse by heat from said longplasma arc column into molten and gaseous products.

8. The method of claim 7 including chemically reacting a selected gaswith said molten and gaseous products.

9. The method of claim 8 wherein said gas comprises an oxidizing gas.

10. The method of claim 7 including the step of recovering energy fromsaid products.

5 3 i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3, 779,13?- Dated December 18, 1973 InventorGQ Salvador L. Camacho It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 66, a parenthesis mark should be inserted before "95percent".

Column 4, line 8, "an oxidation" should be deleted before "dioside" and-carbon should be inserted.

Signed and sealed this 17th day of December 1974.

(SEAL) Attest':

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. An apparatus for reducing by pyrolysis raw unsegregated refusecomprising: a. a furnace chamber; b. a refractory lined hearth in saidfurnace chamber; c. conveyor means adapted to introduce raw unsegregatedrefuse, at least a portion of which is metallic, into said furnacechamber; and d. long arc column forming plasma generator means mountedin said chamber and adapted to initiate and sustain at least one longarc column plasma having a portion thereof in electrical contact withsaid refuse and being adapted to reduce said refuse to gaseous andmolten fluid products by utilization of the column heat.
 2. Theapparatus of claim 1 including gas supply means adapted to contact andchemically react with said gaseous and molten fluid products.
 3. Theapparatus of claim 2 including energy conversion means adapted torecover energy from said products.
 4. The apparatus of claim 2 whereinsaid gas supply means comprises an oxidizing supply.
 5. The apparatus ofclaim 1 wherein said generator means comprises a plurality ofperipherally spaced generators and including electrical circuit meansadapted to initiate a pilot arc in each said generator and enabling amain long arc column to be transferred between at least two saidgenerators and said refuse.
 6. The apparatus of claim 1 includinggroundable electrode means included in said hearth and being adapted toenable a long arc plasma column to be generated between at least onesaid generator and said grounded electrode.
 7. A method for reducing bypyrolysis a volume of raw unsegregated refuse comprising: a. initiallycharging a furnace chamber with refuse materials of which a substantialportion is metallic; b. providing long plasma arc column generationmeans extending through at least one wall portion of said furnacechamber; c. establishing and maintaining at least one long plasma arccolumn between said generation means and said refuse thereby reducing byheat at least said metallic refuse portion to a molten state; d.conveying additional raw unsegregated refuse into said furnace chamber;and e. pyrolyzing all of said raw unsegregated refuse by heat from saidlong plasma arc column into molten and gaseous products.
 8. The methodof claim 7 including chemically reacting a selected gas with said moltenand gaseous products.
 9. The method of claim 8 wherein said gascomprises an oxidizing gas.
 10. The method of claim 7 including the stepof recovering energy from said products.